1. Field of the Invention
The present invention generally relates to a method for forming a low-carbon CVD film for filling STI structures, for example.
2. Description of the Related Art
Conventional gap-filling methods using a cooling susceptor include those using siloxane material and silazane material, where fluidity can be generated easily as a result of bond of Si and hydrocarbon. On the other hand, post-treatment applied after film forming causes carbon to dissociate and the film density in STI trenches to become lower (lower density here refers to opening of numerous void-like holes or shrinking of film in trenches having surface irregularities), while at the same time the film quality also drops (leading to high leak current, poor chemical resistance and other negative results). As a result, problems occur such as the film becoming vulnerable to damage due to exposure to hydrogen fluoride cleaning solution.
In light of the aforementioned problems, the inventors examined materials having less carbon content. When SiH4 and NH3 were combined and the discharge distance in the plasma CVD apparatus was adjusted to 16 mm or less, it was possible to generate fluidity despite the boiling point of SiH4 being −111.9° C. In this case, fluidity could be generated by suppressing the reactivity because the carbon content was zero, and accordingly the viscosity was high and there was dependence on the pattern size. In order to promote fluidity, the inventors also examined the possibility of lowering the viscosity by adding hydrocarbon material or lowering the susceptor temperature. However, the former method was considered inappropriate due to concerns over low density during post-treatment, while the latter method was determined not appropriate, either, because it would increase volatility. Incidentally, the above statements are not provided as known facts, but solely as information that should be explained prior to describing the present invention.
To improve the quality of filling film, it is important to reduce the carbon content in the materials to be used. On the other hand, how to generate fluidity is also an important point. If materials that do not contain carbon are combined, the process parameter margins are expected to narrow if fluidity is to be improved.